In an important apparatus, system or the like required to be constantly in operation, a USP (Uninterruptible Power Supply) is used in some cases in order to continue the power supply to a load even when power supply from a commercial power source is interrupted due to blackout or instantaneous power interruption (or power from a commercial power source is not or cannot be used and these cases are hereinafter collectively referred to as “emergency situation, etc.”). The UPS has a storage battery which stores power to be supplied to the load in an emergency situation, etc., and one UPS may have a plurality of storage batteries.
The storage battery used in the UPS is kept charged and does not operate (discharge) in a normal situation, but operates and supplies power to the load in an emergency situation, etc. It is known that the storage battery degrades over time even in a non-operation state and its degradation is accelerated generally when an ambient temperature is high. Therefore, in the equipment having a storage battery such as the UPS, in order to prevent the occurrence of the case in which the equipment does not operate normally due to the dead battery or the failure of the storage battery, the state of the storage battery is monitored and the remaining battery life is predicted in consideration of the degradation due to the ambient temperature and the service years, and the storage battery is replaced with a new storage battery before the battery reaches the predicted end of the battery life of course when the battery is in a faulty state and even when the storage battery is still in a normal state.
However, in the simple prediction of the remaining life based on the relation between the temperature and a degree of the degradation, since the precision of the prediction of the remaining life is not so high, the storage battery is replaced considerably earlier than the actual end of battery life when taking the safety margin into consideration, and the battery is not used up effectively until the actual end in some cases, so that the use is not efficient from the viewpoint of both of economical use and effective use.
As a technique for solving such a problem, for example, Japanese Patent Application Laid-Open Publication No. 2005-26153 (Patent Document 1) discloses a storage battery monitoring system which detects the temperature T of an assembled battery composed of a plurality of storage batteries, measures the voltage E and the internal resistance R of each storage battery, and determines the service life of each storage battery based on the results of the detection and measurement, so that the end of service life of the storage battery can be accurately determined at high precision while considering other elements in addition to the relation between the temperature and the service life.
Also, the Non-Patent Document 1 describes a battery diagnostic apparatus in which, in order to monitor the state of a lead storage battery used in UPS, the cell voltage, the internal impedance, and the temperature are consecutively measured, and in the measurement of the internal impedance, the internal impedance is measured by using a frequency different from a frequency component of a ripple current generated from the UPS, thereby suppressing the influence of normal mode noises generated from the UPS and stably obtaining the measurement values of the internal impedance.